Acid Catalyzed Addition

The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The acid-catalyzed aldol reaction is depicted in Figure 1. Figure 1. The acid-catalyzed aldol addition reaction of ketones. First, as shown in Figure 2, the acid protonates the ketone molecule to form the protonated ketone. The conjugate base of the acid deprotonates the α carbon of the protonated ketone to form the enol. Figure 2. Formation of the enol.

As depicted in Figure 1, base-catalyzed aldol addition involves adding two carbonyl compounds in aqueous sodium hydroxide to form a β-hydroxy carbonyl compound. Figure 1: The base-catalyzed aldol addition reaction of aldehydes. The reaction preferentially occurs with simple aldehydes, where the α carbon is monosubstituted. The equilibrium of the reaction involving disubstituted aldehydes and ketones shifts backward to the reactants due to the steric interactions at the α carbon. The...

Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the strain present in the ring. This ring strain acts as a driving force for epoxides to undergo ring-opening reactions either with halogen acids or weak nucleophiles in the presence of mild acid. The acid catalyst converts the epoxide oxygen, a poor leaving group, into an oxonium ion, a better leaving group, making the reaction feasible. The...

Stable isotope labeling workflows employing 18O-enriched water (LeO-workflows) are versatile tools for quantitative and qualitative proteomics studies. In protease-assisted (PALeO) workflows, 18O-atoms are introduced by proteolytic cleavage and carboxyl oxygen exchange reactions mediated by proteases. In the acid-catalyzed (ALeO) workflow, 18O-atoms are introduced by carboxyl oxygen exchange at low pH.

Alkenes react with water in the presence of an acid to form an alcohol. In the absence of acid, hydration of alkenes does not occur at a significant rate, and the acid is not consumed in the reaction. Therefore, alkene hydration is an acid-catalyzed reaction. Strong acids, such as sulfuric acid, dissociate completely in an aqueous solution, and the acid participating in the reaction is the hydronium ion. The first step is the slow protonation of an alkene at the less-substituted end to form...